Don Webb of INHS searches for aquatic macroinvertebrates.
Springs are a natural source of groundwater discharge at a rate high enough to form a channel on the earth's surface. The physical and chemical composition of spring water reflects not only the mineral composition of the various rock strata with which the water has been in contact but also the various chemicals that percolate into groundwater. Even though springs provide a unique interface between groundwater and surface water, they have only recently become a focal point of research in Illinois.
Along with their associated seeps and outflow brooks, springs provide a unique habitat for endemic (restricted to a localized area) and relict species of animals and plants because they usually provide a nearly constant physical and chemical environment. Until recently, little emphasis had been given to the study of springs in Illinois, particularly from the perspective of species richness and endemism in relation to water quality. Past studies of springs generally focused on a selected taxonomic group, but provided minimal water quality information other than water temperature, dissolved oxygen, hydrogen ion concentration (as pH), and alkalinity. Aquatic macroinvertebrates of temperate, cold-water areas are dominated by either a noninsectan community (Turbellaria, Annelida, Amphipoda, Isopoda, Gastropoda) or an aquatic insect community (Odonata, Ephemeroptera, Plecoptera, aquatic Diptera, Trichoptera, and aquatic Coleoptera). Faunal dominance by noninsectan species appears in hardwater limestone springs with a pH greater than 7.0 and an alkalinity above 25 mg/L (as CaCO3). Aquatic insects appear to dominate the fauna in both acidic and soft-water springs--those with a pH less than 7.0 and an alkalinity below 25 mg/L.
With the passage of the Clean Water Act of 1972, which called for state funding for groundwater management and water quality programs, states were required to develop biological criteria for the protection of aquatic communities. As recently as 1990, baseline information on the fauna, flora, water quality, and hydrogeology was virtually nonexistent for springs in Illinois. A cooperative program between the Illinois Natural History Survey and the Illinois State Geological Survey was initiated in 1991 to evaluate the current status of Illinois springs, in particular the biota and their relation to groundwater quality. Many locations of springs were determined from topographic maps; additional locations were provided by residents throughout the state. All information on Illinois springs is entered into a computerized database. Early in this century, 88 springs were documented for Illinois. To date, information on 300 springs is included in this database.
Don Webb of INHS searches for aquatic macroinvertebrates.
The majority of Illinois springs are located in the Mississippian, Devonian, and Pennsylvanian limestone and sandstone of the Shawnee Hills and the western border of Illinois. Several springs also originate from the base of the bluffs along the Fox, Illinois, and Rock rivers. Only a few springs, however, are listed from the central plains of Illinois.
Our first intensive survey of Illinois springs focused on seven springs in the Shawnee Hills of southern Illinois. This karst (limestone) region lies outside the areas of intensive agriculture where groundwater contamination from the annual application of agricultural fertilizers and herbicides was expected to be minimal. Thus, the conditions in these springs could be utilized as a benchmark for comparison with other springs in Illinois. Each of these springs was small in size, with a low discharge rate and a substrate consisting generally of sand and small gravel. High concentrations of total dissolved solids and chlorides were measured at Saline Spring and Salt Well Spring, both located in an area of high salinity southeast of Equality in Gallatin County. Springs in this area historically were used as salt wells by native Americans and early settlers. Nitrate nitrogen concentrations were below background levels (1.4 mg/L) and herbicide concentrations were below detection levels.
Eighty-five species of aquatic macroinvertebrates were collected from these seven springs with an average of 27 species per spring. Noninsectan macroinvertebrates dominated this fauna and were species common to most small surface streams in the Shawnee Hills. Oligochaete worms (24 species) represented the most diverse faunal group with Varichaetadrilus angustipenis (Tubificidae) -- rarely collected in Illinois and within a limited distribution in North America -- recorded from six of the springs. Allonais paraguayensis (Naididae) from Old Driver and Salt Well springs, previously known only from Louisiana, South Carolina, and an aquarium in New York, was the most interesting of the species collected. Few aquatic insects were collected and, when present, were low in abundance. The water quality of these springs in the Shawnee Hills is high and the diversity of the aquatic macroinvertebrates is considered low but stable.
A second study focused on 10 karst springs in Monroe and St. Clair counties. This area, often termed "The Sinkhole Plain," is a limestone area with a thin layer of topsoil. Water percolating through the cracks and fissures has dissolved away the limestone, forming an extensive network of underground caves and streams in a pattern resembling a large piece of Swiss cheese and covering two counties. Surface runoff in this area has the opportunity to move quickly through these underground conduits in a matter of hours, rather than taking years to seep slowly through the soil. Geochronologically, these 10 karst springs were assigned to three limestone formations of the Valmeyeran Series of the Mississippian Age. Results from age-dated springs in Monroe and St. Clair counties indicated that these springs were actively discharging water approximately 11,000 years ago.
It was here that a "worst-case scenario" with regard to the biodiversity and water quality was expected. Contamination of these 10 springs from nitrate nitrogen and herbicides was expected to be high, and at levels that would adversely affect the diversity of aquatic macroinve-rtebrates. In addition, aquatic macroinvertebrate species common to surface streams in or adjacent to the study area, and broadly tolerant of environmental perturbations, were expected to occur in these springs.
We collected 141 species of aquatic macroinvertebrates with an average of 42 species per spring. Again, aquatic oligochaetes, amphipods, isopods, and turbellarians were the most abundant macroinvertebrates. Although aquatic insects represented the most diverse group (80 species), their abundance was generally low. Only the mayfly genera Baetis and Stenonema and the caddisfly Cheumatopsyche analis were moderately abundant. Oligochaetes again were the most diverse group of noninsectan organisms (33 species), with both Varichaetadrilus angustipenis and Allonais paraguayensis present in these springs. Another oligochaete, Bratislavia unidentata (Naididae), considered rare in Illinois and uncommon throughout its North American distribution, was collected from Sparrow Spring and its spring-brook.
Mark Wetzel of INHS sampling spring.
Nitrate nitrogen in groundwater is an anion that can be derived from several naturally occurring sources. As an anion, it is not readily adsorbed to soil components, thus it readily migrates through the soil into the groundwater system. Researchers of the llinois State Geological Survey were able to determine a background threshold of 1.4 mg/L for nitrate nitrogen in the karst terrain area of southwestern Illinois based on a previously developed probability technique. Concentrations below 1.4 mg/L were considered natural in their derivation; those above 1.4 mg/L were considered to be of man-made origin. Nitrate nitrogen was present in all 40 water samples collected from the springs, with 39 of the samples reporting levels above the background concentration; however, none exceeded the USEPA Maximum Contaminant Level (USEPA MCL) of 10 mg/L.
At least one of four herbicides (Atrazine, Alachlor, Cyanazine, and Metolachlor) was detected in 33 of the 40 water samples. Atrazine was detected in 73% of the samples; three of these exceeded the USEPA MCL of 3 ug/L. Alachlor was detected in 27.5% of the samples; one exceeded the USEPA MCL of 2 ug/L. Cyanazine was detected in 22.5% of the samples; two of these exceeded the USEPA Health Advisory Limit (USEPA HAL) of 1 ug/L. Metolachlor was detected in 47.5% of the samples. No samples exceeded the USEPA HAL of 100 ug/L.
In general, a "worst-case scenario" regarding the diversity of aquatic macroinvertebrates was not observed in these 10 karst springs. The cave-inhabiting amphipods Crangonyx forbesi and Gammarus troglophilus, and the cave-inhabiting isopod Caecidotea packardi, were collected from seven, eight, and three karst springs, respectively. A positive linear correlation between drainage basin area and aquatic macroinvertebrate species richness was determined for 9 of the 10 springs studied. In comparison, the seven Shawnee Hills springs supported an average of 27 species per spring. Only two amphipod species, Gammarus minus and Gammarus pseudolimnaeus, were collected from springs in the Shawnee Hills; these species are relatively common to surface streams of southern Illinois.
No aquatic macrophytes, little filamentous algae, and no animals or plants listed as endangered or threatened were observed or collected in any of the springs examined in the Shawnee Hills or the Sinkhole Plain.
Research on the springs of Illinois is continuing; numerous springs in the Lincoln Hills Section of western Illinois were sampled during 1996. Springs in the Driftless Area of Northwestern Illinois and the few scattered springs located throughout the Grand Prairie Division of north-central Illinois will be sampled during 1997. This study will allow us to complete an assessment of the community diversity of aquatic macroinvertebrates associated with springs in Illinois, and the relationship of the overall groundwater chemistry with those populations.
D.W. Webb, M.J. Wetzel, and L.R. Phillippe, Illinois Natural History Survey; P.C. Reed and T.C. Young, Illinois State Geological Survey
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